Effects of monotypic diets of soybean, rice, and corn on mallard (Anas platyrhynchos) physiological status

The effects of monotypic diets of agricultural grains on mallard (Anas platyrhynchos) physiological status were tested. Restricted amounts of six diets were fed to captive hen mallards housed in an outdoor aviary at the White River National Wildlife Refuge (Arkansas County, Arkansas, USA). Dietary treatment groups included 1) a 23% protein (high protein) control, 2) a 7% protein (low protein) control, 3) corn, 4) rice, 5) soybeans, and 6) a natural diet, consisting of equal amounts of willow oak acorns (Quercus phellos), Pennsylvania smartweed (Polygonum pennsylvanicum), and Japanese millet (Echinocloa crusgalli) by weight. These diets represent foods available to wild mallards in the Mississippi alluvial valley during winter. Effects of diet on mallard physiological status were determined by measuring body weight at 8 wk and serum metabolites and gamma globulins at 9 wk. No diets induced protein deficiency, as indicated by final equivalent serum total protein and gamma globulin levels among groups fed different diets. The soybean diet, however, caused a negative energy balance as shown by higher serum D-beta-hydroxybutyrate levels.